Hi,
Thank you for contacting us!
We already know about this problem and now we are developing a new plugin version which will be compatible with Gutenberg.
This issue caused by Gutenberg editor (new WordPress editor), using Classic Editor (https://ww.wp.xz.cn/plugins/classic-editor/) you still can to translate posts/pages.
Please follow the next instructions in order to install the Classic Editor (https://ww.wp.xz.cn/plugins/classic-editor/):
1) Go to WordPress admin dashboard;
2) Open Plugins->Add New tab;
3) Then you will see “Classic Editor”, install and activate it, if not – search for Classic Editor plugin (https://prnt.sc/ltggj8);
4) After you activate the Classic Editor plugin, try to translate article;
Let us know about the result.